Add libmoosex-fileattribute-perl to Build-Depends

Required for running tests:

|    dh_auto_test
| Subroutine Sipwise::Base::CLASS redefined at /usr/share/perl5/CLASS.pm line 20.
| Can't locate MooseX/FileAttribute.pm in your Perl library.  You may need to install it
| from CPAN or another repository.  Your library paths are: